The present invention relates to a thread joint between drill string components used in percussive rock drilling operations, and to a male threaded component and a female threaded element used in such components.
A conventional thread joint between two components in a rock drilling equipment for percussive drilling normally has male and female threads cut therein, see for example Eklof et al. U.S. Pat. No. 4,687,368 and Wormald et al. U.S. Pat. No. 4,332,502. During the production of the male thread, a blank of steel is shaped by a threading tool, the blank including an enlarged portion in which the thread is to be formed. The ends of the enlarged portion connect respectively to: (i) a clearance surface or a clearance groove of smaller diameter to receive at least parts of the threading tool, and (ii) a usually conical free end. Then the enlarged portion is provided with a thread in a conventional way, Sharp edges are formed at the thread entrance and exit due to the geometries of the clearance groove and the free end surface. Corresponding sharp edges are formed when cutting a corresponding female thread in another component. The sharp edges cause the male and female threads to damage each other foremost at the respective free end during use of the joint. The conventional thread joint has one or two axially directed support surfaces. When the known thread joint is subjected to bending forces during drilling the thread joint is subjected to bending moments which might lead to fatigue breakage in the threaded portion of the joint. It is usually the damaged male thread that limits the life span of the joint.
One object of the present invention is to provide a thread joint of the above mentioned type, for which a good life span is attained.
Another object of the present invention is to provide a thread joint of the above-mentioned type, in which the life span of the male portion is maximized.
Still another object of the present invention is to provide a thread joint of the above-mentioned type, in which the thread joint can transfer great bending moments without influencing the threads to any great extent.
Still another object of the present invention is to provide a thread joint of the above-mentioned type, in which the thread joint comprises portions that unloads the threads.
The objects of the invention are realized by a thread joint between first and second percussive drilling components. The first component includes a generally cylindrical male thread, and the second component includes a generally cylindrical female thread connected to the male thread to form the thread joint. Each of the male and female threads includes end areas where a radius of the respective thread is smallest. The spigot includes inner and outer conical guiding surfaces disposed adjacent axially inner and outer ends of the spigot. The sleeve includes axially inner and outer conical guiding surfaces disposed adjacent axially inner and outer ends of the spigot, respectively, and arranged to approach respective outer and inner guiding surfaces of the spigot when the spigot enters the sleeve in an impact direction. Each of the conical guiding surfaces of the spigot and the sleeve has a cross section diminishing in the impact direction and defining an apex angle with a center line of the thread joint. The apex angle lies in the range of 1 to 20 degrees.
Another aspect of the invention pertains to a percussive drilling component which includes a spigot having a generally cylindrical male thread formed thereon. The thread includes an axially inner end area and an axially outer free end area, where a radius of the thread is smallest as viewed in a longitudinal cross-section of the spigot. The spigot includes an axially inner conical guiding surface facing toward an axially outer free end of the spigot. The spigot also includes an outer conical guiding surface facing in the same direction as the inner conical guiding surface. The male thread is disposed between the inner and outer conical guiding surfaces. Each of the inner and outer conical guiding surfaces forms an angle with a center line of the spigot. The angle lies in the range of 1 to 20 degrees.
In still another aspect of the invention a percussive drilling component includes a sleeve having a generally cylindrical female thread. The female thread includes axially inner and outer end areas, where a radius of the thread is smallest as viewed in a longitudinal cross-section of the sleeve. The sleeve includes an axially inner conical guiding surface facing toward an axially outer free end of the sleeve. The sleeve also includes an outer conical guiding surface facing in the same direction as the inner conical guiding surface. The female thread is disposed between the inner and outer conical guiding surfaces. Each of the inner and outer conical guiding surfaces forms an angle with a center line of the sleeve. The angle lies in the range of 1 to 20 degrees.